1. Field of the Invention
The present invention relates to a semiconductor device having a structure whereby a direct connection is made between an interconnection board and a semiconductor pellet.
2. Background of the Invention
To improve their portability, there is a desire to make compact electronic circuit devices for video cameras, notebook-size personal computers and the like smaller and lighter, and the achievement of smaller electronic components or electronic components of the same dimensions but a higher level of integration used therein contributes to the achievement of more compact and lightweight electronic circuit devices.
In semiconductor devices, while there has been reduction of the size of a semiconductor pellet and an increase in the level of integration, efforts are not limited to these improvements, and there have been direct connections made from a semiconductor pellet to an interconnection board, thereby improving the mounting density.
An example of this is illustrated in FIG. 9. In this drawing, the reference numeral 1 denotes a semiconductor pellet, which has a large number of bump electrodes 3 formed on a main surface of a semiconductor substrate 2 onto which are large number of electronic elements (not shown in the drawing) are formed. These bump electrodes 3 are generally formed by solder or gold.
The reference numeral 4 denotes an interconnection board, formed by a conductive pattern (not shown in the drawing) of copper formed on a surface of a insulating substrate 5, the conductive pattern being then covered by a photoresist film (not shown in the drawing). Windows are then formed in the photoresist film at positions opposite the bump electrodes 3, so as to expose part of the conductive pattern, thereby forming pad electrodes 6 at the windows. These pad electrodes 6 are generally made of a copper foil of thickness 12 to 18 xcexcm, over which a nickel plating is covered to a thickness of 3 to 5 xcexcm, and further over which gold is laminated to a thickness of 0.03 to 1 xcexcm. In the drawing, however, this is shown as a single layer.
The reference numeral 7 denotes a resin that makes a mechanical connection between the semiconductor pellet 1 and the interconnection board 5, and which protects the interconnection pattern (not shown in the drawing) on the semiconductor pellet 1 from external corrosive gases.
The above-described structure is widely known, and is disclosed in Japanese Unexamined Patent Application publication S63-241955 (prior art 1), U.S. Pat. No. 5,795,818 (prior art 2), Japanese Unexamined Patent Application publication S60-262430 (prior art 3), and Japanese Unexamined Patent Application publication H9-97816 (prior art 4).
Of the above-noted prior art examples, in prior art 1 the bump electrode 3 is formed by solder, and the semiconductor pellet 1 is flip-chip connected to the interconnection board 4.
In the above-noted prior art 2, there is language describing the application of a load of approximately 20 g per bump electrode 3 to the pad electrodes 6, the semiconductor pellet 1 being heated to 240xc2x0 C., and the interconnection board 4 being heated to 190xc2x0 C., with ultrasonic vibration also being applied to the electrodes 3 and 6 so as to make a metal-to-metal joint, and another example noted is that in which a load of approximately 10 g per bump electrode 3 is applied, the semiconductor pellet 1 being heated to 180xc2x0 C. and the interconnection board 4 being heated to 190xc2x0 C., with ultrasonic vibration also being applied to the electrodes 3 and 6 so as to make a metal-to-metal joint.
In both prior art examples 1 and 2, after making a mechanical and electrical joint between the semiconductor pellet 1 and the interconnection board 4, a resin 7 is supplied between the semiconductor pellet 1 and the interconnection board 4 as an adhesive. Because there is a tiny spacing of approximately 100 xcexcm between the semiconductor pellet 1 and the interconnection board 4, however, it is difficult for the resin 7 to enter therebetween, and even if it does enter therebetween, there is the problem of a tendency for air bubbles to remain.
Prior art 1 is such that air bubbles do not remain in the resin 7, but the work involved is troublesome.
In prior art 2, while it can be envisioned that there would be a tendency for air bubbles to remain in the resin 7, there is absolutely no language with regard to how these air bubbles are removed.
In contrast to the above, in prior art examples 3 and 4, a resin 7 is supplied to a region that includes the pad electrodes 6 on the interconnection board 4 beforehand, a semiconductor pellet 1 being supplied to the top of this resin 7 and pressure applied thereto, so that the pad electrodes 6 and the bump electrodes 3 are superposed, thereby forcing the resin 7 from between the bump electrodes 3 and the pad electrodes 6 and making an electrical connection between the electrodes 3 and 6. The applied pressure is maintained in this condition, and resin 7 is cured. After it hardens sufficiently, even if the applied pressure is released, the resin 7 between the semiconductor pellet 1 and the interconnection board 4 makes a mechanical connection, and the pressure between the electrodes maintains the electrical connections.
In the above-noted semiconductor device, because the resin 7 supplied to the top of the interconnection board 4 beforehand is pressed and spread out, it is difficult for air bubble to remain within the resin 7, thereby solving the problem that remained with the prior art examples 1 and 2.
In the prior art example 3, there is language to the effect that when a light-curable resin is used there is absolutely no heat applied to the semiconductor pellet 1 and the interconnection board 4, and even when using a thermally curable resin, the curing temperature is raised to no more than 150xc2x0 C., the result being that it is possible to reduce the thermal distortion of constituent materials, and possible to achieve a connection having high reliability.
In the prior art example 4 as well, there is language to the effect that, although a thermally curable resin 7 is supplied as pressure is applied to join the bump electrodes 3 and the pad electrodes 6, by using a resin 7 that has a curing rate of contraction that is larger than the coefficient of thermal expansion, even in a high-temperature environment because the curing rate of contraction exceeds the coefficient of thermal expansion, force does not act to peel the bump electrodes from the pad electrodes, so that the connection does not become unstable, and language to the effect that, because the end of the bump electrode is in point contact with the pad electrode 6 with pressure applied therebetween, there is further broadening so as to achieve a surface contact, the result being that the resin 7 between the electrodes is driven out from the contacting parts, thereby enabling the achievement of a reliable contact, with no included impurities.
In this manner, in a semiconductor device according to the prior art examples 3 and 4, even after compression deformation is caused within the elastic limit of the bump electrodes 3 superposed with the pad electrodes 6 as the resin 7 is cured, the pressurized contact between the electrodes 3 and 6 is maintained.
The coefficients of thermal expansion of the semiconductor device elements such as semiconductor substrate 2, bump electrodes 3, insulating substrate 5, and pad electrodes 6, in a semiconductor pellet 1 which is based on silicon and an epoxy resin based interconnection board 4, are 2.4 PPM/xc2x0 C., 15 PPM/xc2x0 C., 16 PPM/xc2x0 C., and 20 PPM/xc2x0 C., respectively, and because the coefficients of thermal expansion of the insulating substrate 5, the pad electrodes 6 and the bump electrodes 3 are similar, differences in length caused by thermal expansion do not become a problem.
Although there is a large difference between the coefficients of thermal expansion of the semiconductor substrate 2 and the bump electrodes 3, because the diameters of each bump are small, there is substantially no problem.
However, between the semiconductor pellet 1 and the interconnection board 4 that are adhered by the resin 7, the ratio of coefficients of thermal expansion exceeds 6 and, because the arrangement length of the bump electrodes 3 is considerably long in comparison with the individual bump electrode 3 diameters, when the semiconductor device is operated, causing heating of the semiconductor pellet 1 to above room temperature, there is large difference in thermal expansion between the two adhesion surfaces of the resin 7.
For example, if a semiconductor pellet having an electrode arrangement length of 10 mm is heated to 80xc2x0 C., the electrode arrangement length is lengthened by 1.9 xcexcm, whereas the arrangement length of the pad electrodes 6 is lengthened by 12.8 xcexcm. This length difference caused by thermal expansion is absorbed by the bimetal effect.
In the prior art examples 3 and 4, because the electrodes 3 and 6 are in pressurized contact, when stress caused by thermal expansion in the superposed surface direction is applied, there is position offset in the electrode contact surface, thereby relieving the stress on the electrode contact parts, enabling avoidance of the problem of electrode peeling.
Semiconductor devices in which a fine powder of alumina or silica is dispersed within the resin 7 for the purpose of achieving balance in the differences in thermal expansion are disclosed, for example, in the Japanese Unexamined Patent Application publications H8-195414 (prior art 5), H9-266229 (prior art 6), H10-107082 (prior art 7), and H11-87424 (prior art 8), and in Japanese Patent No. 2914569 (prior art 9) and Japanese Unexamined Patent Application publication H11-40606 (prior art 10).
Of the above, prior art examples, in prior art examples 5 to 9, after making an electrical connection between the semiconductor pellet 1 and the interconnection board 4, resin 7 is supplied to between the respective opposing surfaces. In prior art examples 5 to 8 in particular, there is disclosure of making the filler distribution within the resin 7 at the semiconductor pellet 1 side and interconnection board 4 side different, so as to adjust the thermal expansion coefficients.
In the prior art example 10, there is a disclosure of applying a resin 7 into which a filler is dispersed onto the interconnection board 4 and connecting a semiconductor pellet 1 to this interconnection board 4, the ends of the bump electrodes 3 being made sharp, so that they bite into the pad electrodes 6, thereby achieving a reliable electrical connection without the existence of a filler in the superposed parts of the electrodes 3 and 6.
In the case in which a high level of integration is to be achieved by increasing the number of bump electrodes without increasing the outer dimensions of the semiconductor pellet, the diameters of the bump electrodes 3 are reduced, the arrangement pitch therebetween is narrowed, and the bump electrodes are arranged in a staggered pattern.
If the diameters of the bump electrodes 3 are reduced, however, the variations in the height and shape of the bump electrodes before applying pressure become large.
In the semiconductor device disclosed in prior art examples 3 and 4, because a pressurized contact is achieved because of resilient deformation of the electrode metal, while it is possible to maintain the stable contact condition at high temperatures by virtue of the expansion of the electrodes themselves, at extremely low temperatures, because the boundary of superposition contracts in the peeling direction, the bump electrodes, which originally have a low profile, experience a reduction contact pressure, thereby causing an increase in the contact resistance.
If operation of a semiconductor device using a semiconductor pellet having this type of low bump electrode is started at an extremely low temperature, there is the problem of unstable operation occurring until the semiconductor pellet 1 reaches a sufficiently high temperature.
In particular, when the resin cures, the inorganic filler dispersed within the resin 7 acts as an insulating spacer disposed between the electrodes that have a low force acting between them, and if a tiny amount of resin remains in the space therebetween, this resin acts as a thin-film insulating spacer, thereby causing a faulty electric connection.
If the height of the bump electrodes 3 is reduced by a reduction in the diameter thereof, the limit of elastic deformation when pressure is applied to the superposed parts is lowered, so that if an excessive load is applied plastic deformation tends to occur, after which at extremely low temperatures there is the problem of a sudden increase in contact resistance between the electrodes.
The above-noted problems are particularly prominent when there is a large temperature difference between the time at which operation is started and the temperature after the start of operation, in which case there is a risk of noise being generated between electrodes, and of malfunctioning of the electronic circuit device.
Even with the technology disclosed in the prior art example 10, when the diameter of the bump electrodes 3 is made small in order to accommodate a large number of electrodes, it becomes difficult to make the ends thereof sharp and, because the pad electrode 6 must be covered with a soft metal to a sufficient thickness, immediate application of this technology was not possible from the standpoints of both technology and cost.
Accordingly, the present invention was devised to solve the above-described problems with the prior art, and has as an object to provide a semiconductor device wherein a semiconductor pellet having bump electrodes and an interconnection board having pad electrodes are positioned so as to be mutually opposing, with a resin into which a filler is dispersed and interposing therebetween, and with the bump electrodes and pad electrodes superposed, a hot-pressed connection being made at the superposed electrode parts with filler remaining therebetween, while adhering the semiconductor pellet and the interconnection board together using said resin.
It is another object of the present invention to provide a method for manufacturing a semiconductor device having a step of supplying a resin into which is dispersed a filler onto pad electrodes formed on an interconnection board having an insulating substrate on which a large number of pad electrodes are formed along at least one straight line or onto a region in the vicinity thereof; a step of bringing a semiconductor pellet formed with bump electrodes being capable of diameter thereof to be constricted toward the ends thereof and formed on a semiconductor substrate into opposition with and proximity to an interconnection board, so as to press the resin outward; a step of causing the ends of said bump electrodes to be inserted into the resin, and trapped part of the filler between said ends of said bump electrodes and said pad electrodes; a step of applying pressure so as to crush the end parts of said bump electrodes simultaneously with said resin being removed out of area formed between said superposed electrodes so as to superpose both electrodes; a step of maintaining the pressured condition in the superposed parts between said bump electrodes and said pad electrodes while heating at least said semiconductor pellet so as to thermally press said superposed parts of said each electrodes, and a step of curing said resin so as to adhere said semiconductor pellet and the interconnection board thereby.
In a semiconductor device according to the present invention, part of a filler that is dispersed in a resin that provides adhering between a semiconductor pellet and an interconnection board is caused to remain in the superposed boundary between the hot-pressed and connected bump electrodes and pad electrodes.
The structure of this semiconductor device is one in which part of the filler of a resin is caught between the end parts of bump electrodes formed with a constricted diameter at the end parts made of a soft conductive material and pad electrodes, the end parts of the pad electrodes being crushed so as to cause outward swelling of the periphery of the superposed part.
In the semiconductor device according to the present invention, filler is caused to remain in 50% or more of the superposed parts of the bump electrodes and pad electrodes, thereby maintaining a good electrical connection at all the electrode superposed parts.
Because if the filler is concentrated in a lump in a region smaller than 10% of the surface area of the superposed parts, there is a deterioration of electrode superposing strength and reduction of thermal joining strength in the region surrounding the region of the remaining filler, filler should be dispersed so as to cause the filler to remain in at least 10% or more of the superposed surface area between the bump electrodes and the pad electrodes.
Additionally, by making the area rate of filler in surface area of the superposed parts between the bump electrodes and the pad electrodes in which filler remains be 10% or less, it is possible to achieve good thermal adhesion to obtain a good electrical and mechanical connection.
By using particulate or fibrous filler as the filler that is dispersed in the resin used in a semiconductor device according to the present invention, it is possible to make minimum the surface area for cutting off heat and current.
In the method for manufacturing a semiconductor device according to the present invention, resin into which is dispersed a filler is first supplied over an interconnection board, and the bump electrodes of a semiconductor pellet are inserted into this resin, so that part of the filler in the resin remains at the electrode superposition boundary between the bump electrodes and the pad electrodes as a hot-pressed joint is made between the superposed parts, this method enabling the setting of the heating temperature of the semiconductor pellet to within the range 230xc2x0 C. to 300xc2x0 C. and the setting of the heating temperature of the interconnection board to within the range 50xc2x0 C. to 120xc2x0 C.